This invention relates to a process and apparatus for the large-scale production of pre-coated microscope slides.
Pre-coated microscope slides have, in principle, been known for a long time. They are microscope slides coated with a layer of a dyestuff suitable for the purposes of microscopy. When a drop of liquid material to be stained is applied to such a microscope slide, then, after a certain period of time, the staining process commences.
The oldest examples of pre-colored microscope slides are those coated with brilliant cresyl blue for the so-called supravital staining of reticulocytes. They are prepared by manually coating microscope slides with a 1% alcoholic solution of brilliant cresyl blue, followed by drying. A drop of blood is smeared on to a so-treated microscope slide, which, after keeping for about 10 minutes in a moist chamber, is covered with a cover slip and then examined microscopically (cf, Pschyrembel, Klinisches Worterbuch, Berlin, 1969, p. 1287).
Pre-colored microscope slides have recently been described in U.S. Pat. No. 3,906,120 which are coated with new methylene blue (methylene blue N) and cresyl violet acetate. They are used for staining erythrocytes and leukocytes and give a differential blood count. This patent also describes, for the same purpose, microscope slides pre-coated with the dyestuffs methylene azure blue, methylene blue NN, cresyl violet acetate and toluidine blue O.
In all these cases, the dyestuffs are applied from an organic or aqueous solution in a thin film to the microscope slides and then dried. However, because of the inadequate wetting which sometimes occurs, this process gives rise to difficulties. Therefore, U.S. Pat. No. 3,906,120 requires the additional use of surface-active agents in order to avoid such wetting difficulties. The use of surface-active agents is admittedly possible in the case therein described but, in other cases, these agents could have a disturbing effect on the sensitive staining processes. A further disadvantage of all previously known pre-coated microscope slides is that hitherto they could only be produced manually in small numbers and, of course, considerable variations in quality had to be taken into account.